Two sphere of same material have radii r1 and r2. They are heated to same temperature and kept in same enclosure at low temperature their rates of loss of heat are in the ratio
$\dfrac{r_2^2}{r_1^2}$
$\dfrac{r_1^2}{r_2^2}$
$\dfrac{r_{1}}{r_{2}}$
$\dfrac{r_{2}}{r_{1}}$